Solid state image pickup device and manufacturing method thereof

ABSTRACT

A method of manufacturing a solid state image pickup device including photoelectric conversion elements which are two-dimensionally arranged in a semiconductor substrate, and a color filter having a plurality of color filter patterns differing in color from each other and disposed on a surface of the semiconductor substrate according to the photoelectric conversion elements. The method including the steps of successively subjecting a plurality of filter layers differing in color from each other to a patterning process to form the plurality of color filter patterns. At least one color filter pattern to be formed at first among the plurality of color filter patterns is formed by means of dry etching, and the rest of the plurality of the color filter pattern is formed by means of photolithography.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of PCT Application No.PCT/JP2006/302061, filed Feb. 7, 2006, which was published under PCTArticle 21(2) in Japanese.

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2005-034620, filed February 10,2005; and No. 2005-034621, filed Feb. 10, 2005, the entire contents ofboth of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a solid state image pickup device representedby a photoelectric conversion element such as a C-MOS, CCD, etc., andalso to a method for manufacturing the solid state image pickup device.In particular, this invention relates to a color filter to be configuredin conformity with a photoelectric conversion element.

2. Description of the Related Art

A solid state image pickup device, such as a CCD, C-MOS, etc., which isadapted to be mounted in a digital camera has been increasingly enhancedin terms of the number of pixel (picture elements) as well as thefineness of pixels in recent years. In the case of a solid state imagepickup device having especially fine pixels, the pixel size is reducedto a level of less than 2 μm×2 μm.

Further, the solid state image pickup device is now configured to havecolor filters corresponding to photoelectric conversion elements,thereby enabling it to reproduce full color. As for the method offorming the color filter, there has been generally employed a techniqueof forming a pattern by means of photolithography process (see forexample, JP Patent Laid-open Publication (Kokai) No. 11-68076 (1999).

Meanwhile, the region (aperture) which is available to the photoelectricconversion element of solid state image pickup device for thephotoelectric transferring is limited to about 20 to 40% based on theentire area of the solid state image pickup device though it depends onthe size of the solid state image pickup device and on the number ofpixel. Therefore, as the aperture is small in size, it will inevitablyresult in the deterioration of sensitivity of the solid state imagepickup device. In order to make up for this problem, it is generallypracticed to provide a condensing micro-lens over the photoelectricconversion element.

However, there has been increasing demand in recent years for a highlyrefined solid state image pickup device having as many pixels of notless than six millions and hence the size of pixel of color filter to bemounted together with the solid state image pickup device is, in manycases, confined to a level of less than 2 μm×2 μm. This in turn raises aproblem that due to insufficient resolution of the color filter to beformed by means of photolithography process, the properties of the solidstate image pickup device are badly affected. This insufficiency ofresolution is manifested as color uneven originating from themalformation of pattern as the size of pixel becomes as small as notmore than 2.5 μm or around 1.8 μm.

Namely, as the size of pixel becomes smaller, the aspect ratio ofpattern becomes larger (the thickness of pattern becomes larger relativeto the width thereof), so that it is impossible to completely eliminatea portion of color filter that should be essentially eliminated (aportion other than the effective region of pixel), thus permitting it toremain as a residue giving an adverse influence to the pixels of othercolors. With a view to overcome this problem, a method has been tried toprolong the developing time. However, this raises another problem thatwhen the developing time is prolonged, a portion of the color filter(pixel) that has been cured and essentially required to remain may bealso peeled away.

Further, in the case of the patterning by means of photolithography,there will be raised a phenomenon that the edge portion of pattern ofcolor filter is caused to rise (i.e., a horn-like edge is caused to begenerate). Especially when the size of pixel becomes smaller, theproperties of the color filter would be adversely affected by thishorn-like edge, giving rise to the generation of color uneven.

If it is desired to secure satisfactory spectral characteristics, itwould be inevitable to increase the film thickness of the color filter.When the film thickness of the color filter is increased, the edgeportion of the pattern of color filter tends to become roundish as thefineness of the pixel is further advance, thus more likely deterioratingthe resolution of the color filter. The color filter is generally formedby making use of a photosensitive resin incorporating color pigments.Therefore, when the concentration of pigments included in color filterlayers is increased, a quantity of light which is required for thephoto-setting reaction of the resin may not reach to the bottom of thecolor filter layers, thus making it impossible to sufficiently cure thephotosensitive resin. As a result, there will be raised a problem thatthe color filter layers may be peeled off in the developing process ofphotolithography and hence defective pixels would be caused to begenerated.

Furthermore, when the color filter is formed thick, in addition to theaforementioned problems involved in the manufacturing process thereof,there is another problem that the light entering obliquely into aportion of the color filter pattern may be permitted to pass, through aneighboring portion of the color filter pattern, into a photoelectricconversion element, thus raising problems such as mixing of colors anddeterioration of sensitivity. This problem becomes more prominent as thesize of pixel of the color filter becomes smaller.

In view of the aforementioned phenomena, when it is desired to increasethe number of pixel of the solid image pickup element, the problem whichis important to deal with is how to make thinner the color filter layerin addition to achieving a highly refined pattern of the color filter.

Incidentally, the problem of color mixing of incident light would beraised even in a case where the distance between the color filter andthe photoelectric conversion element is relatively large.

The decrease of aperture ratio of the micro-lens (i.e., decrease ofphotosensitivity) to be mounted on the highly refined solid state imagepickup device and also the deterioration in quality of image due to theincrease of noise such as flare and smear are now becoming great issuesto be dealt with. Therefore, it has been considered necessary to enhancethe converging property of incident light entering into thephotoelectric conversion element by making use of micro-lens and tominimize the under-lens distance for enhancing the S/N ratio at thephotoelectric conversion element. If the under-lens distance isrelatively large, a couple of problems will be raised as follows.

First, if the under-lens distance is relatively large, the uptake angleof incident light becomes smaller, so that the quantity of incidentlight is decreased, thus providing a dark display as a whole. Secondary,in the case of a camera using a photoelectric conversion element such asa CMOS or CCD, the angle of incident light is generally caused to changedepending on the magnitude of diaphragm (F number) of the objectivelens. Therefore, when the diaphragm is actuated to move to the full openside, oblique incident light is caused to increase, thus deterioratingthe converging property of incident light and hence deteriorating thesensitivity of the photoelectric conversion element. Additionally, sincethe angle of incident light is caused to differ prominently between acentral portion and a peripheral portion of the pixel region ofsemiconductor chip where a photoelectric conversion element is formed,the quantity of incident light entering into the pixels (photoelectricconversion elements) of the peripheral portion is caused to decrease,thus presenting a dark display at the peripheral portion of the displaypicture.

The color filter is generally formed on a flattening layer that has beenformed in advance on a semiconductor substrate for the purpose ofenhancing the adhesion of the color filter to the underlying layer.However, if it is desired to minimize the aforementioned under-lensdistance and to miniaturize the solid state image pickup device, it isdesirable to dispense with the flattening layer. However, since a colorresist to be employed in the photolithography process is poor inadhesion to a semiconductor substrate, it will be peeled away in thedeveloping step. Therefore, it has been considered difficult to dispensewith the flattening layer.

With a view to overcoming this problem, there has been proposed a methodwherein the surface of semiconductor substrate is treated with chemicalsso as to introduce a functional group exhibiting excellent bondingproperty to a resin into the surface of semiconductor substrate. Evenwith this method however, it has been impossible to secure a sufficientadhesion of the color filter to the surface of semiconductor substrate.

Meanwhile, the color filter is generally constituted by filters of threeprimary colors, i.e., blue, green and red filters. There has been aproblem however in designing the solid state image pickup device that,due to the characteristics of coloring material, a green resist forforming the green filter is lower in refractive index after the curingthereof as compared with a red resist and a blue resist to be employedfor forming the red filter and the blue filter, respectively. Namely,since the color resist to be employed in the photolithography process isrequired to be excellent in photosensitivity, it is difficult to selectone which is also high in refractive index after the curing thereof,thus creating a discrepancy in refractive index among these threedifferent color filters. Because of this discrepancy, the lightconverging effect by the micro-lens is also caused to differ among thesecolor filters, thus raising a problem that non-uniformity of reflectanceis caused to be generated among these color filters.

As described above, the color filter to be created by means of theconventional photolithography process is accompanied with variousproblems that it is impossible to secure sufficient resolution, thatresidues of color filter tends to remain unremoved, that the peeling ofpixel is more likely to occur, and that the characteristics of the solidstate image pickup device may be deteriorated. Additionally, there arealso problems that not only the distance between the color filter andthe photoelectric conversion element but also the distance between themicro-lens and the photoelectric conversion element (under-lensdistance) is caused to become large.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a solid state imagepickup device having a color filter which can be formed withoutgenerating malformation of pattern, without leaving the residue ofpattern, and without generating the peeling of pattern, which can beformed close to the photoelectric conversion element, and which is freefrom non-uniformity in reflectance among the pixels.

Another object of the present invention is to provide a method ofmanufacturing such a solid state image pickup device as described above.

According to a first aspect of the present invention, there is provideda method of manufacturing a solid state image pickup device comprisingphotoelectric conversion elements which are two-dimensionally arrangedin a semiconductor substrate, and a color filter including a pluralityof color filter patterns differing in color from each other and disposedon a surface of the semiconductor substrate according to thephotoelectric conversion elements; the method comprising successivelysubjecting a plurality of filter layers differing in color from eachother to a patterning process to form said plurality of color filterpatterns; wherein at least one color filter pattern to be formed atfirst among said plurality of color filter patterns is formed by meansof dry etching; and the rest of said plurality of the color filterpattern is formed by means of photolithography.

According to a second aspect of the present invention, there is provideda method of manufacturing a solid state image pickup device comprisingphotoelectric conversion elements which are two-dimensionally arrangedin a semiconductor substrate, a color filter including a plurality ofcolor filter patterns differing in color from each other and disposed ona surface of the semiconductor substrate according to the photoelectricconversion elements, and a flattening layer formed entirely or partiallyon the surface of the semiconductor substrate; the method comprisingsuccessively subjecting a plurality of filter layers differing in colorfrom each other to a patterning process to form said plurality of colorfilter patterns; wherein at least one color filter pattern to be formedat first among said plurality of color filter patterns is formed bydry-etching an unnecessary portion of one of the filter layers and aportion of the flattening layer which is formed below the unnecessaryportion; and the rest of said plurality of color filter pattern isformed by means of photolithography.

According to a third aspect of the present invention, there is provideda solid state image pickup device comprising: photoelectric conversionelements which are two-dimensionally arranged in a semiconductorsubstrate; and a color filter including a plurality of color filterpatterns differing in color from each other and disposed on a surface ofthe semiconductor substrate according to the photoelectric conversionelements; wherein said plurality of color filter patterns comprise onecolor filter pattern containing a thermally cured resin, and the rest ofsaid plurality of color filter patterns containing a photo-cured resin.

According to a fourth aspect of the present invention, there is provideda solid state image pickup device comprising: photoelectric conversionelements which are two-dimensionally arranged in a semiconductorsubstrate; and a color filter including a plurality of color filterpatterns differing in color from each other and disposed on a surface ofthe semiconductor substrate according to the photoelectric conversionelements; wherein one of the color filter patterns which is the largestin area among said plurality of color filter patterns contains athermally cured resin, the rest of said plurality of color filterpatterns containing a photo-cured resin.

According to a fifth aspect of the present invention, there is provideda solid state image pickup device comprising: photoelectric conversionelements which are two-dimensionally arranged in a semiconductorsubstrate; a color filter including a plurality of color filter patternsdiffering in color from each other and disposed on a surface of thesemiconductor substrate according to the photoelectric conversionelements; and a flattening layer formed entirely or partially on thesurface of the semiconductor substrate; wherein the flattening layerformed below said plurality of color filter patterns is composed of twoportions differing in thickness from each other, one portion beingdisposed below one of said plurality of color filter patterns and theother portion being disposed below the rest of said plurality of colorfilter patterns.

According to a sixth aspect of the present invention, there is provideda solid state image pickup device comprising: photoelectric conversionelements which are two-dimensionally arranged in a semiconductorsubstrate; a color filter including a plurality of color filter patternsdiffering in color from each other and disposed on a surface of thesemiconductor substrate according to the photoelectric conversionelements; and a flattening layer formed entirely or partially on thesurface of the semiconductor substrate; wherein the color filter isconstituted by one filter pattern which is formed on the flatteninglayer and another filter pattern which is formed directly on thesemiconductor substrate.

According to a seventh aspect of the present invention, there isprovided a solid state image pickup device comprising: photoelectricconversion elements which are two-dimensionally arranged in asemiconductor substrate; a color filter including a plurality of colorfilter patterns differing in color from each other and disposed on asurface of the semiconductor substrate according to the photoelectricconversion elements; and a flattening layer formed entirely or partiallyon the surface of the semiconductor substrate; wherein said plurality ofcolor filter patterns include one color filter pattern containing athermally cured resin, the rest of said plurality of color filterpatterns containing a photo-cured resin.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1A is a cross-sectional view illustrating a process of patterningby means of dry etching to be employed in the present invention;

FIG. 1B is a cross-sectional view illustrating a process of patterningby means of dry etching to be employed in the present invention;

FIG. 1C is a cross-sectional view illustrating a process of patterningby means of dry etching to be employed in the present invention;

FIG. 1D is a cross-sectional view illustrating a process of patterningby means of dry etching to be employed in the present invention;

FIG. 1E is a cross-sectional view illustrating a process of patterningby means of dry etching to be employed in the present invention;

FIG. 2A is a cross-sectional view illustrating a process of patterningby means of photolithography to be employed in the present invention;

FIG. 2B is a cross-sectional view illustrating a process of patterningby means of photolithography to be employed in the present invention;

FIG. 2C is a cross-sectional view illustrating a process of patterningby means of photolithography to be employed in the present invention;

FIG. 3 is a cross-sectional view illustrating part of the solid stateimage pickup device that has been obtained by a manufacturing methodaccording to one embodiment of the present invention;

FIG. 4A is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toone embodiment of the present invention;

FIG. 4B is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toone embodiment of the present invention;

FIG. 4C is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toone embodiment of the present invention;

FIG. 4D is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toone embodiment of the present invention;

FIG. 4E is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toone embodiment of the present invention;

FIG. 4F is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toone embodiment of the present invention;

FIG. 4G is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toone embodiment of the present invention;

FIG. 5 is a plan view illustrating part of the solid state image pickupdevice shown in FIG. 3;

FIG. 6 is a cross-sectional view illustrating part of the solid stateimage pickup device according to another embodiment of the presentinvention;

FIG. 7 is a cross-sectional view illustrating part of the solid stateimage pickup device according to another embodiment of the presentinvention;

FIG. 8A is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 8B is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 8C is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 8D is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 8E is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 8F is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 8G is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 8H is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 8I is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according toanother embodiment of the present invention;

FIG. 9A is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according tostill another embodiment of the present invention;

FIG. 9B is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according tostill another embodiment of the present invention;

FIG. 9C is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according tostill another embodiment of the present invention;

FIG. 9D is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according tostill another embodiment of the present invention;

FIG. 9E is a cross-sectional view illustrating in step-wise themanufacturing method of a solid state image pickup device according tostill another embodiment of the present invention;

FIG. 10 is a microphotograph illustrating green patterns of variouspixel sizes which have been formed, via a flattening layer, on thesurface of a test pattern substrate;

FIG. 11 is a microphotograph illustrating green patterns of variouspixel sizes which have been formed, via a flattening layer, on thesurface of a test pattern substrate;

FIG. 12 is a microphotograph illustrating a green pattern 1.5 μm inpixel size that has been formed by means of photolithography on thesurface of a glass substrate;

FIG. 13 is a microphotograph illustrating a green pattern 2.0 μm inpixel size that has been formed by means of photolithography on thesurface of a glass substrate; and

FIG. 14 is a microphotograph illustrating a green pattern 2.0 μm inpixel size that has been formed by means of dry etching on the surfaceof a glass substrate.

DETAILED DESCRIPTION OF THE INVENTION

Next, best mode for carrying out the present invention will beexplained.

A method of manufacturing a solid state image pickup device according toa first aspect of the present invention is featured in that at least onecolor filter pattern to be formed at first among a plurality of colorfilter patterns is formed by means of dry etching and the rest of theplurality of the color filter pattern(s) is (are) formed by means ofphotolithography.

Since it is impossible to secure sufficient adhesion between aphotoresist and a semiconductor substrate, when a filter pattern isformed directly on the surface of a semiconductor substrate by means ofphotolithography, there will be raised a problem that the photoresist iscaused to peel off on the occasion of developing step. Whereas, in thecase of dry etching, a resinous resin used for manufacturingsemiconductor chips to be employed as a color filter can be freelyselected from those which are higher in resolution than the color resistand excellent in adhesion to the semiconductor substrate. Therefore, itis possible to create, as a first pattern, a fine and smooth filterpattern without leaving the residue thereof and without generating thepeeling of pattern on the occasion of patterning step.

If the filter patterns of the rest of colors including the second colorare subsequently formed by means of dry etching, the surface of thefilter pattern that has been once formed may be roughened unless anysuitable means is provided for protecting the surface of the filterpattern formed in advance, thus raising a problem. Further, there isalso a problem that a color filter layer to be subsequently formed maybe badly affected by the roughened surface of the filter pattern thathas been formed in advance.

In view of these problems, at least a first color filter pattern isformed by means of dry etching and the rest of the color filterpattern(s) is (are) formed by means of photolithography. Morespecifically, a first color filter pattern is formed by means of dryetching and the color filter patterns of the rest of colors includingthe second color are formed by means of photolithography.

By taking these measures, it is now possible, without necessitating anyspecial protection for the surface of the filter pattern of the firstcolor, to prevent the surface of the filter pattern of the first colorfrom being roughened in the step of patterning the rest of the colorfilters including the second color filter by means of photolithography.Further, since the rest of filter patterns after the second color filterpattern can be firmly sustained by the filter pattern of the first colorthat has been strongly adhered to an underlying layer, it is possible toprevent the rest of filter patterns from being peeled on the occasion ofthe developing step thereof. Namely, since the filter pattern that hasbeen formed by means of dry etching is enabled to act as an anchor, itis possible to prevent the filter patterns that have been formed bymeans of photolithography from being cut out.

Additionally, since the accuracy of the filter pattern that has beenformed at first has a great influence on the accuracy of the colorfilter as a whole, when at least the filter pattern to be formed atfirst is formed by making use of dry etching, it is possible to enhancethe accuracy of the color filter as a whole, thus making it possible toobtain a solid state image pickup device which is free from color unevenand provided with a large number of pixels.

As described above, according to the first aspect of the presentinvention, since at least the first pattern-forming step for forming apattern of color filter layer is performed by means of dry etching, theresist used for manufacturing semiconductor chips to be employed as amask can be freely selected from those which are capable of achievingvery fine patterning. Accordingly, it is possible to create a colorfilter having a fine pattern excellent in configuration without leavingthe residue thereof and without generating the peeling of pixel. Namely,according to this method, since a color filter layer that has beenthermally cured is dry-etched, thereby making it possible, in thebeginning, to form a predetermined filter pattern which is excellent inadhesion to a substrate, even if the next filter pattern is subsequentlyformed adjacent to the first filter pattern, it is possible to preventthis neighboring next filter pattern from being peeled off owing to theexistence of the first filter pattern formed at first and excellent inadhesion. Moreover, since the filter pattern that has been formed atfirst is completely cured, it cannot be peeled off in a developingprocess to be subsequently performed by means of photolithography.

A method of manufacturing a solid state image pickup device according toa second aspect of the present invention is featured in that at leastone color filter pattern to be formed at first among a plurality ofcolor filter patterns is formed by dry-etching an unnecessary portion ofone of the filter layers and a portion of the flattening layer which isformed below said unnecessary portion, and that the rest of theplurality of color filter pattern(s) is (are) formed by means ofphotolithography.

As described above, according to the second aspect of the presentinvention, since at least one color filter pattern to be formed at firstamong a plurality of color filter patterns is formed by dry-etching, itis possible to obtain almost the same effects as described above in themethod of manufacturing a solid state image pickup device according tothe first aspect of the present invention.

Incidentally, the filter patterns are generally configured such that,since the spectral characteristics desired of each of the color filterpatterns differ depending on the kind of color and also since the kindsof resin and pigment to be employed in these color filter patternsdiffer depending on the kind of color, the thickness of each of thesefilter patterns is caused to differ from the others. Further, since thefilter pattern to be formed by means of dry etching is not required tobe photosensitive, the concentration of pigment in the filter patterncan be increased. As a result, this filter pattern may be formed thinneras compared with other filter patterns to be formed by means ofphotolithography.

Accordingly, by allowing the flattening layer to be dry-etched on theoccasion of dry-etching the first filter pattern, it is possible tominimize a difference in thickness among these filter patterns,especially a difference in thickness between the filter pattern to beformed by means of dry etching and the filter pattern to be formed bymeans of photolithography. As a result, it is now possible to provide asolid state image pickup device provided with a color filter having asurface which is minimal in step portion between neighboring colorfilter patterns and also very small in distance between the color filterand the photoelectric conversion element.

As described above, according to the second aspect of the presentinvention, it is possible to provide a method of manufacturing a solidstate image pickup device provided with a color filter which isexcellent in fineness, free from the residue and chipping of filterpatterns, excellent in smoothness of edge portion, minimal in stepportion between neighboring color filter patterns and also very small indistance between the color filter and the photoelectric conversionelement.

In the method of manufacturing a solid state image pickup deviceaccording to the second aspect of the present invention, the step ofdry-etching one of the filter layers may be performed in such a mannerthat a portion of the flattening layer which is formed below anunnecessary portion is not completely etched away leaving therein theflattening layer having a reduced thickness, whereby the flatteninglayer existing below the aforementioned one of the color filter layersis made to have a different thickness from that of the flattening layerexisting below the rest of color filter patterns.

Further, the step of dry-etching one of the filter layers may beperformed in such an extent that the unnecessary portion as well as aportion of the flattening layer which is formed below the unnecessaryportion is completely etched away, exposing the surface of semiconductorsubstrate.

Due to the roughened surface of the flattening layer that may begenerated in the step of dry etching, it is more likely that theresidues of filter pattern resists of other colors to be deposited afterthe dry etching are allowed to leave behind. There are manypossibilities that these residues may badly affect the quality ofpicture, generating noise or defects as the distance between the filterpattern and the photoelectric conversion element becomes smaller.Therefore, the existence of these residues is not desirable. Thegeneration of these residues can be prevented by completely eliminatingthe flattening layer and then depositing the filter patterns directly onthe surface of the semiconductor substrate by means of photolithography.More specifically, the etching is continued until the flattening layercan be completely removed on the occasion of the dry etching, thusleaving no flattening layer below the filter patterns to be subsequentlyformed by means of photolithography.

In the method of manufacturing a solid state image pickup deviceaccording to the first and the second aspects of the present invention,one of the color filter patterns which is the largest in area among theplurality of color filter patterns may be formed by means of dryetching.

When a filter pattern which is the largest in area among the pluralityof filter patterns is created by means of dry etching, the rest offilter patterns to be created by means of photolithography can beeffectively sustained. Additionally, the accuracy of the filter patternwhich is the largest in area among the plurality of filter patterns hasgreat influence on the accuracy of the color filter as a whole.

Furthermore, when these filter patterns are constructed as a multi-layerstructure, it would be effective to apply dry etching to a lower filterpattern (which is disposed close to the semiconductor substrate).

Additionally, it may be preferable that the color filter layer to bepatterned by means of dry etching contains at least a thermosettingresin, and the color filter layer to be patterned by means ofphotolithography contains at least a photo-setting resin.

Since the filter pattern containing a thermosetting resin and formedinto a predetermined pattern by means of dry etching is enabled tofirmly adhere to the semiconductor substrate or the flattening layer,there is little possibility that the filter pattern is caused to peeloff. Further, in the case of the color filter layer containing athermosetting resin, it is possible to increase the concentration ofcoloring material contained therein, thus making it possible to makethinner the color filter, to prevent the mixing of colors that may becaused by the incident light and to reduce the thickness of the solidstate image pickup device.

The solid state image pickup device according to the third aspect of thepresent invention is featured in that a plurality of color filterpatterns comprise one color filter pattern containing a thermally curedresin, and the rest of the plurality of color filter patterns containinga photo-cured resin.

In the case of the solid state image pickup device constructed asdescribed above, since the color filter comprises a color filter patterncontaining a thermally cured resin, it is possible to secure excellentadhesion between the color filter and the semiconductor substratewithout necessitating the interposition of the flattening layer, therebymaking it possible to deposit the color filter directly on the surfaceof the semiconductor substrate without any deposition in advance of theflattening layer. As a result, it is possible to obtain a solid stateimage pickup device which is very small in under-lens distance.Especially, since a thermosetting resin is employed, it is possible toincrease the concentration of a coloring material in the solid matter,thus making it possible to reduce the thickness of the color filter andhence to prevent the mixing of colors that may be caused by the incidentlight. Because of these reasons also, it is possible to obtain a solidstate image pickup device wherein the distance between the color filterand the photoelectric conversion element is very small, and theunder-micro-lens distance is also very small, thus enabling it toexhibit excellent sensitivity. Additionally, the problem of color uneventhat may be caused by the configuration of the edge of pattern of colorfilter can be overcome.

The aforementioned plurality of color filter patterns may include agreen filter pattern which contains a resin exhibiting a higherrefractive index than that of resins contained in the rest of colorfilter patterns. In this way, the refractive indexes of the plurality ofcolor filter patterns can be made nearly the same with each other. As aresult, the light converging effect by the micro-lens can be madeidentical with other, thus making it possible to obtain an excellentsolid state image pickup device.

Further, since a resin which is relatively high in refractive indextends to indicate a smaller etching rate, to perform the patterning of alayer containing a resin exhibiting a high refractive index by means ofdry etching is effective in obtaining a filter pattern having a smoothsurface.

Furthermore, a flattening layer may be formed on the color filter so asto eliminate the projected/recessed portions on the surface of the colorfilter and then micro-lens may be formed on this flattening layer.

In addition to the formation of the micro-lens on the color filter, aperipheral portion of the micro-lens, or a lower portion of themicro-lens may be constituted by part of the color filter, i.e., anupper portion of the color filter. By constructing the micro-lens inthis manner, the under-micro-lens distance can be decreased, thus makingit possible to obtain a solid state image pickup device which isexcellent in sensitivity.

The solid state image pickup device according to the fourth aspect ofthe present invention is featured in that one of the color filterpatterns which is the largest in area among a plurality of color filterpatterns contains a thermally cured resin, and the rest of the pluralityof color filter patterns contains a photo-cured resin.

In the case of the solid state image pickup device constructed asdescribed above, since a color filter pattern having a largest areaamong a plurality of color filter patterns contains a thermally curedresin, it is possible to secure excellent adhesion between the colorfilter pattern and the semiconductor substrate. Further, since theflattening layer can be dispensed with, it is possible to obtain a solidstate image pickup device which is very small in under-lens distance.Especially, since a thermosetting resin is employed, it is possible toincrease the concentration of a coloring material in the solid matter,thus making it possible to reduce the thickness of the color filter andhence to prevent the mixing of colors that may be caused by the incidentlight. Because of these reasons also, it is possible to obtain a solidstate image pickup device wherein the distance between the color filterand the photoelectric conversion element is very small, and theunder-micro-lens distance is also very small, thus enabling it toexhibit excellent sensitivity. Additionally, the problem of color uneventhat may be caused by the configuration of the edge of pattern of colorfilter can be overcome.

When a filter pattern is formed directly on the surface of semiconductorsubstrate by making use of a photo-setting resin (photoresist), therewill be raised a problem that the filter pattern is caused to peel offon the occasion of developing process since the photoresist fails tohave sufficient adhesion to the semiconductor substrate. Whereas, in thecase of the solid state image pickup device according to the third andthe fourth aspects of the present invention, since the thermally curedfilter pattern is enabled to act as an anchor, the photo-cured filterpattern that has been formed adjacent to the thermally cured filterpattern can be prevented from being cut out. Therefore, it is possibleto form a color filter directly on the surface of semiconductorsubstrate without necessitating the provision of the flattening layer.Accordingly, it is possible to minimize the distance between the colorfilter and the photoelectric conversion element as well as the distancebetween the micro-lens and the photoelectric conversion element(under-lens distance).

The solid state image pickup device according to the fifth aspect of thepresent invention is featured in that the flattening layer formed belowa plurality of color filter patterns is composed of two kinds of layersdiffering in thickness from each other, one of which is disposed belowone of the plurality of color filter patterns and the other beingdisposed below the rest of the plurality of color filter patterns.

In the case of the solid state image pickup device constructed asdescribed above, since any difference in thickness between the filterpatterns can be absorbed by the flattening layer, it is possible toprovide a solid state image pickup device provided with color filtershaving a uniform flat surface.

In the case of the solid state image pickup device constructed asdescribed above, the aforementioned plurality of color filter patternsmay include a green filter pattern which contains a resin exhibiting ahigher refractive index than that of resins contained in the rest of thecolor filter patterns.

By setting the refractive index of the resin to be contained in thegreen filter pattern higher than the refractive index of the resincontained in the rest of the color filter patterns, the refractiveindexes among the filter patterns can be made nearly the same with eachother. As a result, it is possible to obtain an excellent solid stateimage pickup device where the light converging effect by the micro-lenson each of the color filters can be made identical to other.

Further, since a resin which is relatively high in refractive indextends to indicate a smaller etching rate, the technique of performingthe patterning of a layer containing a resin exhibiting a refractiveindex by means of dry etching is effective in obtaining a filter patternhaving a smooth surface.

Further, the solid state image pickup device may further comprisemicro-lenses disposed directly or indirectly over the color filters andaccording to the photoelectric conversion elements, the peripheralportion (a lower portion) of the micro-lens being constituted by aportion (an upper portion) of the color filters.

As described above, since a peripheral portion of the micro-lens isconstituted by part of the color filter, it is possible to obtain asolid state image pickup device where the under-micro-lens distance isrelatively small.

The solid state image pickup device according to the sixth aspect of thepresent invention is featured in that the color filter is constituted byone kind of filter pattern which is formed, via the flattening layer, onthe semiconductor substrate and another kind of filter pattern which isformed directly on the semiconductor substrate.

In the case of the solid state image pickup device constructed asdescribed above, since any difference in thickness between the filterpatterns can be absorbed by the flattening layer, it is possible toprovide a solid state image pickup device which is provided with colorfilters having a uniform flat surface and wherein the flattening layeris disposed at only the least limited portions which necessitate theprovision of the flattening layer, thus minimizing the distance betweenthe color filter and the photoelectric conversion element.

The solid state image pickup device according to the seventh aspect ofthe present invention is featured in that a plurality of color filterpatterns comprise one color filter pattern containing a thermally curedresin, and the rest of the plurality of color filter patterns containinga photo-cured resin.

In the case of the solid state image pickup device constructed asdescribed above, since the filter pattern containing a thermosettingresin is enabled to firmly adhere to the semiconductor substrate or theflattening layer, there is little possibility that the filter pattern iscaused to peel off. Further, in the case of the color filter layercontaining a thermosetting resin, it is possible to increase theconcentration of coloring material contained therein, thus making itpossible to make thinner the color filter, to prevent the mixing ofcolors that may be caused by the incident light and to reduce thethickness of the solid state image pickup device.

Next, various specific embodiments of the present invention will beexplained on the basis of aforementioned various aspects of the presentinvention.

First of all, a couple of processes for forming a filter pattern, whichcan be employed in the present invention, will be explained.

A process for performing the patterning by means of dry etching whichwill be employed in the present invention can be carried out in such amanner that a pattern of resin having a configuration of an object isformed on the surface of an object-forming layer, and the object-forminglayer is dry-etched with this resin pattern being employed as a mask,thereby transcribing this configuration of the object to theobject-forming layer. More specifically, as shown in FIGS. 1A to 1E, acolor filter layer 32 is formed as an object-forming layer on thesurface of a substrate 31 (FIG. 1A), a photosensitive resin layer 33 isformed on the color filter layer 32 (FIG. 1B), this photosensitive resinlayer 33 is then patterned to form a resin pattern 34 having aconfiguration of an object (FIG. 1C), and the configuration of thisresin pattern 34 is transcribed onto the color filter layer 32 by dryetching with the resin pattern 34 being employed as a mask (FIG. 1D),thus finally forming a filter pattern 35 having the configuration of theobject (FIG. 1E).

A process for performing the patterning by means of photolithographywhich will be employed in the present invention can be carried out insuch a manner that a photosensitive object-forming layer is formed atfirst and then subjected to a patterning exposure to selectivelyphoto-cure the object-forming layer through a mask, and then theresultant object-forming layer is subjected to a developing process,thereby removing an unnecessary portion of the object-forming layer toobtain a patterned object. More specifically, as shown in FIGS. 2A to2C, a color filter layer 42 is formed as an object-forming layer bymaking use of a photosensitive resin composition (FIG. 2A) and thensubjected to a patterning exposure to selectively photo-cure the colorfilter layer 42 through a mask (not shown) to selectively cure theobject-forming layer (FIG. 2B), and then an unnecessary portion 42 b isremoved by making use of a developing solution to leave photo-curedportions 42 a, which is followed, if necessary, by heat curing, thusforming a filter pattern 43, i.e., the object (FIG. 2C).

FIG. 3 is a cross-sectional view illustrating part of the solid stateimage pickup device according to one embodiment of the presentinvention. FIGS. 4A-4G are cross-sectional views each illustrating instep-wise the manufacturing method of a solid state image pickup deviceshown in FIG. 3. FIG. 5 is a plan view of the solid state image pickupdevice shown in FIG. 3.

As shown in FIG. 3, the solid state image pickup device according to oneembodiment of the present invention is constituted by a color filter 12for color-separating an incident light which is formed on the surface ofa semiconductor substrate 10 provided therein with photoelectricconversion elements 11 which are arranged two-dimensionally and capableof converting the light into electrical signals; a flattening layer 13employed for flattening the surface of the color filter 12; and aplurality of micro-lenses 14 disposed on this flattening layer 13. Thisflattening layer 13 may be omitted under some circumstances.

This solid state image pickup device can be manufactured according tothe method shown in FIGS. 4A-4G.

First of all, as shown in FIG. 4B, a first color resist layer 22 isformed on the surface of a semiconductor substrate 20 provided withphotoelectric conversion elements 21 which are two-dimensionallyarranged thereon (see FIG. 4A). This first color resist layer 22 can beformed as follows. Namely, a first resin dispersion comprising, as amajor component, a thermosetting resin, and a pigment is coated on thesurface of the semiconductor substrate 20 and then thermally cured toform the first color resist layer 22.

Then, as shown in FIG. 4C, by means of photolithography for example, aprescribed resin pattern 23 is formed on this first color resist layer22. As for the material for the resin pattern 23, it is possible toemploy a photosensitive resin such as acrylic resin, epoxy resin,polyimide resin, phenol novolac resin. These resins can be employedsingly or as a combination thereof or as a copolymer thereof. As for thelight exposure apparatus to be employed in the photolithography processfor patterning the photosensitive resin, there are known various kindsof apparatuses such as a stepper, an aligner, a mirror projectionaligner. However, the stepper is generally employed for the formation ofcolor filter of the solid state image pickup device where a large numberof pixels and an increased fineness are required.

Then, as shown in FIG. 4D, by making use of the resin pattern 23 as amask, the first color resist layer 22 is patterned by means of dryetching to form a first filter pattern 24 a. As for the method of dryetching, it is possible to employ, for example, ECR, a parallel platemagnetron, DRM, ICP, double-frequency type RIE, etc.

The gas to be employed in the dry etching may be a reactive (oxidizingor reductive) gas, i.e., a gas having etching properties. For example,it is possible to employ, though is not limited to, a gas containing, inits molecule, a halogen such as fluorine, chlorine, bromine, etc.; or agas containing, in its molecule, an oxygen or sulfur atom.

Subsequently, a second color resist layer is deposited all over thesurface and then patterned in the same manner as in the case of thefirst filter pattern 24 a by means of dry etching or photolithography toform a second filter pattern 24 b as shown in FIG. 4E.

Then, a third color resist layer is deposited all over the surface andthen patterned by means of photolithography to form a third filterpattern (not shown), thereby fabricating a color filter 25 comprisingthe first, the second and the third filter patterns.

FIG. 5 illustrates the arrangement of each of the filter patterns of thecolor filter 25. The arrangement shown in FIG. 5 is a so-called Bayerarrangement wherein a green (G) filter is disposed at every secondpixel, whereas both a red (R) filter and a blue (B) filter are disposedbetween a couple of G filters and at every second line. FIG. 3 is across-sectional view taken along the line A-A′ of FIG. 5.

Then, as shown in FIG. 4F, a flattening layer 26 is deposited on thecolor filter 25 which has been fabricated as described above. As for thematerial for the flattening layer, it is possible to employ acrylicresin, epoxy resin, polyimide resin, phenol novolac resin, polyesterresin, urethane resin, melamine resin, styrene resin, etc. These resinscan be employed singly or in combination of two or more kinds thereof.Incidentally, this flattening layer 26 may not necessarily be provided.

Finally, as shown in FIG. 4G, micro-lenses 27 are formed on theflattening layer 26 by means of thermal reflow method which isconventionally known, thereby accomplishing the manufacture of the solidstate image pickup device.

According to the manufacturing method of the solid state image pickupdevice as described above, since the first filter pattern 24 a is formedby way of the patterning using dry etching after the first color resistlayer 22 has been completely thermally cured, the adhesion of the firstfilter pattern 24 a to the semiconductor substrate 20 is very strong.Due to the provision of the first filter pattern 24 a which is excellentin adhesion as described above, even if the second and the third filterpatterns are formed by means of photolithography, these second and thirdfilter patterns can be firmly sustained by the first filter pattern 24 awhich has been placed adjacent to them, thereby making it possible toimprove the adhesion of the color filter 25 as a whole. Therefore, thesefilter patterns can be formed directly on the surface of thesemiconductor substrate 20 without necessitating the interposition ofthe flattening layer.

In this case, the first filter pattern 24 a should preferably beconstituted by a filter pattern having the largest area among aplurality of filter patterns. In this way, it is possible to furtherenhance the adhesion of the color filter to the semiconductor substrate.The size of the area of the filter pattern having the largest area maybe 1-2 times as large as that of the filter pattern having the smallestarea among a plurality of filter patterns. Additionally, since thefilter pattern having the largest area has been patterned by means ofdry etching, it is possible to more accurately perform the patterning ofthe filter pattern having the largest area, thereby making it possibleto enhance the accuracy of the color filter as a whole. Morespecifically, the green filter pattern is more likely to be selected ashaving the largest area.

Further, when a color filter having a higher concentration of pigment,i.e., a color filter having a lower content of a resin having much to dowith the curing of the color filter is patterned by means of dryetching, even the color filter layer which cannot be sufficiently curedin the ordinary photolithography can be patterned accurately withoutleaving the residue thereof and without generating the peeling thereof.When a color filter having a high concentration of a pigment ispatterned by means of photolithography, the shape of edge of the filterpattern tends to become defective, thus giving rise to the generation ofuneven image. However, when such a color filter is patterned by means ofdry etching, it is possible to form the filter pattern which isexcellent in configuration of edge, thus obviating the generation of anuneven image. More specifically, these effects would be more prominentlymanifested when the dry etching is applied to the formation of a redfilter pattern or a green filter pattern.

When the size of a color filter is very small (especially, when the sizeis not more than 2.5 μm), the color filter should preferably bepatterned by means of dry etching. Namely, when the ordinaryphotolithography is applied to the patterning of a color filter of sucha very small size, the shape of edge of the filter pattern tends tobecome defective, thus giving rise to the generation of uneven image.However, when such a color filter is patterned by means of dry etching,it is possible to form the filter pattern which is excellent inconfiguration of edge. Incidentally, when the first color filter isformed to have an excellent configuration, the configuration of the restof color filters including the second color filter can be improved andthe peeling thereof can be also prevented.

Additionally, the patterning by means of dry etching is also useful inthe patterning of such a kind of color filter that exhibits a lowtransmissivity to the exposure wavelength to be employed in thepatterning by means of photolithography, resulting in insufficientexposure and hence leading to the deterioration of resolution and thegeneration of peeling. Namely, by making use of the dry etching, eventhe color filter layer which cannot be sufficiently cured in theordinary photolithography can be patterned accurately without leavingthe residue thereof and without generating the peeling thereof.Especially, these effects would be more prominently manifested when thedry etching is applied to the formation of a blue filter pattern.

Irrespective of the reasons, when the first filter pattern is formed bymeans of dry etching, it is possible to obtain a filter pattern which isexcellent in resolution, capable of strongly adhering to the underlyingsubstrate, and free from residues and peeling. Thereafter, thephotolithography which is small in the number of steps and excellent inefficiency can be employed for the patterning for the rest of filterlayers. As a result, it is possible, due to the filter pattern that hasbeen formed at first with high accuracy and enabled to strongly adhereto the substrate, to form the rest of filter layers accurately andwithout generating the peeling thereof even if they are patterned bymeans of photolithography.

When a color filter is to be formed by means of photolithography, astepper apparatus using an exposure light having a wavelength of 365 nmcan be employed. In the case of the blue filter, since the exposurelight having a wavelength of 365 nm is incapable of penetrating into thebottom portion of the filter, a bottom portion of the blue colorsensitive resin cannot be sufficiently cured, thereby permitting theblue filter to be easily peeled as compared with the filters of othercolors.

In the present invention however, since a pattern (especially, a greenpattern) which is excellent in configuration and adhesion is formedfirst, if a subsequently formed pattern is poor in adhesion, such as ablue filter pattern formed by means of photolithography, it is possibleto prevent the peeling and defective configuration of the blue filterpattern as the blue filter pattern is sustained by the green pattern.The arrangement of colors of the solid state image pickup device isgenerally based on the Bayer arrangement wherein one unit cell isconstituted by four pixels, i.e., two green pixels, one blue pixel andone red pixel. Therefore, when the green filter is formed by means ofdry etching, the other two color filter can be supported by the greenfilter, thereby improving the configuration and adhesion of the othertwo color filters.

Various kinds of green patterns varying in pixel size were formed,directly or through a flattening layer, on a test pattern substrate bymeans of photolithography or by means of dry etching to evaluate theadhesion and the generation of peeling in these green patterns. Theresults are summarized in the following Table 1.

Incidentally, the criterion for evaluation was as follows.

TABLE 1 Evaluation on adhesion Underlying Pixel size (μm) CF-formingmethod layer 1.0 1.5 2.0 2.5 3.0 Photolithography Direct to X X X X Xsubstrate Flattening X Δ ◯ ◯ ◯ layer Dry etching Direct to ◯ ◯ ◯ ◯ ◯substrate Flattening ◯ ◯ ◯ ◯ ◯ layer ◯: Peeling was not recognized Δ:Peeling was recognized more or less X: Pixel was not adhered

It will be recognized from Table 1 that in the case where the greenpattern was formed directly on the substrate by means ofphotolithography, the green patterns of any pixel size were foundincapable of satisfactorily adhering to the substrate. Even if the greenpattern was formed, through the flattening layer, on the substrate bymeans of photolithography, the green patterns having a size of not lessthan 2.0 μm were found capable of satisfactorily adhering to thesubstrate and the green pattern having a size of 1.5 μm was foundincapable of preventing the peeling thereof from the substrate. Whereas,in the case of the dry etching method, it was found successful inpreventing the peeling of every green patterns irrespective of manner ofdeposition, i.e., deposition directly on the surface of the substrate ordeposition with the interposition of the flattening layer, and even thegreen pattern having a pixel size of 1.0 μm was found successful inpreventing the peeling thereof.

It will be recognized from these results that when the filter pattern ofthe first color is formed by means of etching and then the filterpatterns of the rest of colors including the second color are formed bymeans of photolithography, it is possible to obtain a color filter whichis excellent in adhesion as a whole, since the filter patterns of therest of colors can be sustained by the filter pattern of the first colorwhich is excellent in adhesion.

Incidentally, FIGS. 10 and 11 show respectively a microscopic photographillustrating green patterns of various pixel sizes which were formed,via a flattening layer, on the surface of a test pattern substrate. FIG.10 shows a microscopic photograph of patterns formed by means ofphotolithography and FIG. 11 shows a microscopic photograph of patternsformed by means of etching method. As shown by the mark “B” in FIG. 10,when photolithography was employed, the peeling of pixels was caused tobe generated at a pixel size of 1.5 μm. Whereas, when etching method wasemployed, the peeling of pixels was not caused to be generated even thepixel size was reduced to as small as 1.0 μm as shown in FIG. 11.

Next, rectangular green patterns were formed on a glass substrate bymeans of photolithography and dry-etching method to assess theconfigurations thereof. FIGS. 12 and 13 both show microscopicphotographs of green patterns having a pixel size of 1.5 μm and a pixelsize of 2.0 μm, respectively, and formed by means of photolithography.FIG. 14 shows a microscopic photograph of green pattern having a pixelsize of 2.0 μm and formed by means of dry-etching method. It will berecognized from FIGS. 12, 13 and 14 that while the green patterns formedby means of photolithography indicated prominently the generation ofdefective configuration (especially, as shown by the mark “C” of FIG.12), the green pattern formed by means of dry-etching method indicatedexcellent configuration.

Since there is a problem when filter patterns are successively formed bymeans of dry etching that the roughness of the filter pattern that hasbeen formed at first would give adverse influence to the color filterlayers to be formed subsequently, it is preferable that when a colorfilter is consisted of three colors, the first color filter patternshould be formed by making use of dry etching, and when a color filteris consisted of four colors, the first color filter pattern or the firstand the second color filter patterns should be formed by making use ofdry etching, the rest of the color filters being formed by making use ofphotolithography in either cases.

Further, the resin to be contained in the green filter pattern may beselected so as to have a higher refractive index as compared with theresins to be contained in the blue and the red filter patterns.Conventionally, there has been a problem that since the refractive indexof the green filter pattern is lower than the refractive indexes ofother color filter patterns, the reflectance of the color filter becomesnon-uniform. When it is desired to increase the refractive index of thegreen filter pattern, it may be conceivable to employ a resin having ahigher refractive index. However, because of the restriction that theresin is subjected to photolithographic process, the freedom to select asuitable resin is very narrow and hence it has been very difficult toselect a resin having a higher refractive index.

Whereas according to the method proposed by this aspect of theinvention, since the green filter pattern can be formed by means of dryetching without necessitating the employment of photolithography, it isnow possible to select the resin for the green filter pattern fromvarious kinds of thermosetting resins exhibiting a higher refractiveindex.

As described above, when the resin to be contained in the green filterpattern is selected to have a higher refractive index as compared withthat of the resins to be contained in the blue and the red filterpatterns, the refractive indexes of these three color filters can bemade nearly identical with each other. As a result, the light convergingeffect by the micro-lens can be made identical with other, thus makingit possible to obtain an excellent solid state image pickup device.

Further, since a resin which is relatively high in refractive indextends to indicate a smaller etching rate, to perform the patterning of alayer containing a resin exhibiting a high refractive index by means ofdry etching is effective in obtaining a filter pattern having a smoothsurface.

In order to enable the refractive indexes of these color filter patternsto become almost identical with each other, the resin to be used in thegreen filter pattern should preferably be selected from those having arefractive index which is about 0.05 to 0.2 higher than that of theresins to be employed in other filter patterns.

Incidentally, as for the resin to be contained in the blue and the redfilter patterns, it is possible to employ those having a refractiveindex ranging from 1.5 to 1.6 such as epoxy resin, polyimide resin,phenol novolac resin, polyester resin, urethane resin, melamine resin,urea resin, styrene resin, etc. As for the resin to be contained in thegreen filter pattern, it is possible to employ those having a refractiveindex ranging from 1.55 to 1.7 such as acrylic resin, epoxy resin,polyimide resin, phenol novolac resin, polyester resin, urethane resin,melamine resin, urea resin, styrene resin, a mixed resin containing oneor more kinds of these resins such as a copolymer thereof. Inparticular, it is possible, for the purpose of achieving a highrefractive index, to employ phenol resin, polystyrene resin, a polymeror monomer having benzene ring or aromatic ring introduced therein andalso to employ acrylic resin having a halogen atom or sulfur atomintroduced into the skeleton thereof.

As another aspect of the invention, as shown in FIG. 6, the micro-lens27 may be formed directly on the surface of the color filter 25 and thena boundary portion between the neighboring filter patterns may be etcheddown to a depth of 0.03 μm-0.5 μm from the surface thereof. According tothis structure, since the peripheral portion (lower portion) of themicro-lens is constituted by part (upper portion) of the color filter25, it is possible to minimize the under-micro-lens distance, thusmaking it possible to obtain a solid state image pickup device which isexcellent in sensitivity.

Incidentally, the reason for setting the lower limit of the depth to bedug down at the boundary portion between the neighboring filter patternsto 0.03 μm is that this value is the minimum value which SEM or AFM caneffectively identify the thickness thereof. On the other hand, thereason for setting the upper limit thereof to 0.5 μm is that if thedepth (step portion) is exceeded over 0.5 μm, the surface of film wouldbe roughened giving rise to the generation of surface scattering, thusdeteriorating the sensitivity. Furthermore, when this depth is exceededover 0.5 μm, the effective film thickness of the color filter may become1 μm or more for instance, thus rendering it contrary to one of theobjects of the present invention to make thinner the color filter.

FIG. 7 is a cross-sectional view illustrating part of the solid stateimage pickup device according to still another embodiment of the presentinvention. FIGS. 8A-8I are cross-sectional views each illustrating instep-wise the manufacturing method of a solid state image pickup deviceshown in FIG. 7. The plan view of FIG. 7 is identical with that shown inFIG. 5.

As shown in FIG. 7, the solid state image pickup device is constitutedby a flattening layer 52 having a step portion and formed on asemiconductor substrate 50 provided therein with photoelectricconversion elements 51 which are arranged two-dimensionally and capableof converting the light into electric signals; a color filter 53 whichis employed for color-separating an incident light and formed on thesurface of the flattening layer 52; and a plurality of micro-lens 54disposed on this color filter 52.

This solid state image pickup device can be manufactured according tothe method shown in FIGS. 8A-8I.

First of all, as shown in FIG. 8B, the first flattening layer 62 isformed on the surface of semiconductor substrate 60 provided withphotoelectric conversion elements 61 which are two-dimensionallyarranged thereon (see FIG. 8A). As for the materials for this flatteninglayer, it is possible to employ acrylic resin, epoxy resin, polyimideresin, phenol novolac resin, polyester resin, urethane resin, melamineresin, urea resin, styrene resin, a mixed resin containing one or morekinds of these resins.

Then as shown in FIG. 8C, a green resist layer 63 is formed on thesurface of the first flattening layer 62. This green resist layer 63 canbe formed as follows. Namely, a resin dispersion comprising, as a majorcomponent, a thermosetting resin, and a green pigment is coated on thesurface of the first flattening layer 62 and then thermally cured toform the green resist layer 63.

Then, as shown in FIG. 8D, by means of photolithography for example, aprescribed resin pattern 64 is formed on this green resist layer 63. Asfor the material for the resin pattern 64, it is possible to employ aphotosensitive resin such as acrylic resin, epoxy resin, polyimideresin, phenol novolac resin. These resins can be employed singly or as acombination thereof or as a copolymer thereof. As for the light exposureapparatus to be employed in the photolithography process for patterningthe photosensitive resin, it is possible to employ those explained withreference to the step of the aforementioned embodiment shown in FIG. 4C.

Then, as shown in FIG. 8E, by making use of the resin pattern 64 as amask, the green resist layer 63 is patterned by means of dry etching toform a green filter pattern 65 a. On this occasion, an unnecessaryportion of the green resist layer is removed and also an upper portionof the flattening layer which is located below the unnecessary portionof the green resist layer is removed.

As for the method of dry etching, it is possible to employ, for example,ECR, a parallel plate magnetron, DRM, ICP, double-frequency type RIE,etc.

The gas to be employed in the dry etching may be a reactive (oxidizingor reductive) gas, i.e., a gas having etching properties. For example,it is possible to employ, though not limited, a gas containing, in itsmolecule, a halogen such as fluorine, chlorine, bromine, etc.; or a gascontaining, in its molecule, oxygen or sulfur atom.

Subsequently, a blue filter pattern 65 b and a red filter pattern (notshown) are successively formed by means of photolithography to form acolor filter 66 comprising the green, the blue and the red filterpatterns as shown in FIG. 8F.

FIG. 5 illustrates the arrangement of each of the filter patterns of thecolor filter 66. The arrangement shown in FIG. 5 is a so-called Bayerarrangement wherein every other pixel is a green (G) filter, and whereinthe green (G) filters are alternated with red (R) filters in the oddrows and blue (B) filters in the even rows (or vice versa). FIG. 7 is across-sectional view taken along the line A-A′ of FIG. 5.

Then, as shown in FIG. 8G, a second flattening layer 67 is deposited onthe color filter 66 which has been fabricated as described above. As forthe material for the second flattening layer, it is possible to employacrylic resin, epoxy resin, polyimide resin, phenol novolac resin,polyester resin, urethane resin, melamine resin, styrene resin, etc.These resins can be employed singly or in combination of two or morekinds thereof.

Then, as shown in FIG. 8H, a lens-shaped mother die 68 is formed on thesurface of the second flattening layer 67 by means of the known thermalreflow method. As for the material for the lens-shaped mother die 68, itis possible to preferably employ a photosensitive resin. For example,resins excellent in alkaline solubility and thermal reflow property suchas acrylic resin, phenol resin, polystyrene resin, etc. can be employed.

Finally, by making use of this lens-shaped mother die 68 as a mask, adry etching treatment was performed, thereby transcribing theconfiguration of this lens-shaped mother die 68 to the second flatteninglayer 67, thus forming micro-lens 69. On this occasion, a boundaryportion between the neighboring patterns of the color filter 66 wasetched away from the surface to a depth ranging from 0.03 μm to 0.5 μm,thereby accomplishing the manufacture of the solid state image pickupdevice where a lower portion of the micro-lens is constituted by anupper portion of the color filter as shown in FIG. 8I.

In the manufacturing method of the solid state image pickup device asdescribed above, since the green filter pattern 65 a is formed by meansof dry etching after the green resist layer 63 has been completelythermally cured, there is little possibility of generating defectivepixels in the developing step to be carried out in a subsequentphotolithography process.

In the embodiment explained above, the green filter pattern 65 a shouldpreferably be constituted by a filter pattern having the largest areaamong a plurality of filter patterns. By doing so, it is possible tofurther enhance the adhesion of the green filter pattern to anunderlying substrate and to effectively prevent the generation ofdefective pixels. The size of the area of the green filter patternhaving the largest area may be 1-2 times as large as that of the filterpattern having the smallest area among a plurality of filter patternsfor instance. Additionally, since the filter pattern having the largestarea has been patterned by means of dry etching, it is possible to moreaccurately perform the patterning of the filter pattern having thelargest area, thereby making it possible to enhance the accuracy of thecolor filter as a whole. More specifically, the green filter pattern ismore likely to be selected as having the largest area.

Further, when a color filter having a higher concentration of pigment,i.e., a color filter having a lower content of a resin having much to dowith the curing of the color filter is patterned by means of dryetching, even the color filter layer which cannot be sufficiently curedin the ordinary photolithography can be patterned accurately withoutleaving the residue thereof and without generating the peeling thereof.More specifically, these effects would be more prominently manifestedwhen the dry etching is applied to the formation of a red filter patternor a green filter pattern.

Additionally, the patterning by means of dry etching is also useful inthe patterning of such a kind of color filter that exhibits a lowtransmissivity to the exposure wavelength to be employed in thepatterning by means of photolithography, resulting in insufficientexposure and hence leading to the deterioration of resolution and thegeneration of peeling. Namely, by making use of the dry etching, eventhe color filter layer which cannot be sufficiently cured in theordinary photolithography can be patterned accurately without leavingthe residue thereof and without generating the peeling thereof.Especially, these effects would be more prominently manifested when thedry etching is applied to the formation of a blue filter pattern.

Irrespective of the reasons, when the first filter pattern is formed bymeans of dry etching, it is possible to obtain a filter pattern which isexcellent in resolution, capable of strongly adhering to the underlyingsubstrate, and free from residues and peeling. Thereafter, thephotolithography which is small in the number of steps and excellent inefficiency can be employed for the patterning for the rest of filterlayers. As a result, it is possible, due to the filter pattern that hasbeen formed at first with high accuracy and enabled to strongly adhereto the substrate, to form the rest of filter layers accurately andwithout generating the peeling thereof even if they are patterned bymeans of photolithography.

Since there is a problem when filter patterns are successively formed bymeans of dry etching that the roughness of the filter pattern that hasbeen formed at first would give adverse influence to the color filterlayers to be formed subsequently, it is preferable that when a colorfilter is consisted of three colors, the first color filter patternshould be formed by making use of dry etching, and when a color filteris consisted of four colors, the first color filter pattern or the firstand the second color filter patterns should be formed by making use ofdry etching, the rest of the color filters being formed by making use ofphotolithography in either cases.

Further, the resin to be contained in the green filter pattern may beselected so as to have a higher refractive index as compared with theresins to be contained in the blue and the red filter patterns.Conventionally, there has been a problem that since the refractive indexof the green filter pattern is lower than the refractive indexes ofother color filter patterns, the reflectance of the color filter becomesnon-uniform. When it is desired to increase the refractive index of thegreen filter pattern, it may be conceivable to employ a resin having ahigher refractive index. However, because of the restriction that theresin is subjected to photolithographic process, the freedom to select asuitable resin is very narrow and hence it has been very difficult toselect a resin having a higher refractive index.

Whereas according to the method proposed by this aspect of theinvention, since the green filter pattern can be formed by means of dryetching without necessitating the employment of photolithography, it isnow possible to select the resin for the green filter pattern fromvarious kinds of thermosetting resins exhibiting a higher refractiveindex.

As described above, when the resin to be contained in the green filterpattern is selected to have a higher refractive index as compared withthat of the resins to be contained in the blue and the red filterpatterns, the refractive indexes of these three color filters can bemade nearly identical with each other. As a result, the light convergingeffect by the micro-lens can be made identical with other, thus makingit possible to obtain an excellent solid state image pickup device.

Further, since a resin which is relatively high in refractive indextends to indicate a smaller etching rate, to perform the patterning of alayer containing a resin exhibiting a high refractive index by means ofdry etching is effective in obtaining a filter pattern having a smoothsurface.

In order to enable the refractive indexes of these color filter patternsto become almost identical with each other, the resin to be used in thegreen filter pattern should preferably be selected from those having arefractive index which is about 0.05 to 0.2 higher than that of theresins to be employed in other filter patterns.

Incidentally, as for the resin to be contained in the blue and the redfilter patterns, it is possible to employ those having a refractiveindex ranging from 1.5 to 1.6 such as epoxy resin, polyimide resin,phenol novolac resin, polyester resin, urethane resin, melamine resin,urea resin, styrene resin, etc. As for the resin to be contained in thegreen filter pattern, it is possible to employ those having a refractiveindex ranging from 1.55 to 1.7 such as acrylic resin, epoxy resin,polyimide resin, phenol novolac resin, polyester resin, urethane resin,melamine resin, urea resin, styrene resin, a mixed resin containing oneor more kinds of these resins such as a copolymer thereof. Inparticular, it is possible, for the purpose of achieving a highrefractive index, to employ phenol resin, polystyrene resin, a polymeror monomer having benzene ring or aromatic ring introduced therein andalso to employ acrylic resin having a halogen atom or sulfur atomintroduced into the skeleton thereof.

Further, as shown in FIG. 8I, since a boundary portion between theneighboring filter patterns is dug down to a depth of 0.03 μm-0.5 μmfrom the surface thereof and the peripheral portion of the micro-lens isconstituted by part of the color filter 66 in the step of forming themicro-lens, it is possible to minimize the under-micro-lens distance,thus obtaining a solid state image pickup device which is excellent insensitivity.

Incidentally, the reason for setting the lower limit of the depth to bedug down at the boundary portion between the neighboring filter patternsto 0.03 μm is that this value is the minimum value which SEM or AFM caneffectively identify the thickness thereof. On the other hand, thereason for setting the upper limit thereof to 0.5 μm is that if thedepth is exceeded over 0.5 μm, the surface of film would be roughenedgiving rise to the generation of surface scattering, thus deterioratingthe sensitivity. Furthermore, when this depth is exceeded over 0.5 μm,the effective film thickness of the color filter may become 1 μm or morefor instance, thus rendering it contrary to one of the objects of thepresent invention to make thinner the color filter.

Next, the present invention will be more specifically explained withreference to various embodiments of the present invention.

EXAMPLE 1

The method of manufacturing the solid state image pickup deviceaccording to this example will be explained with reference to FIGS. 4Ato 4G.

A pigment-dispersed green resist was spin-coated at a rotational speedof 1000 rpm on the surface of a semiconductor substrate 20 provided withphotoelectric conversion elements 21 which are two-dimensionallyarranged as shown in FIG. 4A. Then, the coated layer was baked for 6minutes at a temperature of 230° C. to form a green resist layer 22 asshown in FIG. 4B. On this occasion, a green pigment represented by acolor index of C.I.PG36 was employed at a concentration of 35 wt % andthe film thickness of the green resist layer 22 was 0.6 μm. Further, athermosetting acrylic resin was employed as a resin or a major componentof the green resist.

Then, a coating solution containing an acrylic photosensitive resin as amajor component was spin-coated on the surface of the green resist layer22 at a rotational speed of 3000 rpm and then formed into a pattern bymeans of photolithography to obtain a resin pattern 23 as shown in FIG.4C. Subsequently, by making use of this resist pattern 23 as a mask, thegreen resist layer 22 was subjected to an etching treatment by makinguse of a flon gas in a dry etching apparatus, thus forming a greenfilter pattern 24 a as shown in FIG. 4D. The film thickness of the greenfilter pattern 24 a on this occasion was 0.8 μm.

Then, by making use of a pigment-dispersed blue resist and by way of thesame patterning method using dry etching as employed for the greenfilter pattern 24 a, a blue filter pattern 24 b was formed as shown inFIG. 4E. On this occasion, pigments represented, respectively, by acolor index of C.I.PB156 and a color index of C.I.PV23 were employed inthe blue resist at a concentration of 40 wt % and the film thickness ofthe blue resist layer 22 was 0.8 μm. Further, a thermosetting acrylicresin was employed as a resin or a major component of the blue resist.

Subsequently, by making use of a pigment-dispersed red resist and by wayof photolithography, a red filter pattern (not shown) was formed toobtain a color filter 25. On this occasion, pigments having,respectively, a color index of C.I.PR117, a color index of C.I.PR48:1and a color index of C.I.PY139 were employed in the red resist at aconcentration of 45 wt % and the film thickness of the red resist layer22 was 0.8 μm.

Further, a coating solution containing acrylic resin was spin-coated onthe surface of color filter 25 formed as described above at a rotationalspeed of 1000 rpm. Then, the coated layer was heat-treated for 10minutes over a hot plate at a temperature of 200° C., thereby curing theresin to form a flattening layer 26 as shown in FIG. 4F.

Finally, as shown in FIG. 4G, a micro-lens 27 was formed on the surfaceof the flattening layer 26 by means of the conventional thermal reflowmethod, thus accomplishing a solid state image pickup device.

In the case of the solid state image pickup device thus obtained, sincethe color filter 25 was directly formed on the surface of thesemiconductor substrate 20 and furthermore since a thermosetting resinwas employed to thereby make it possible to increase the concentrationof coloring material in a solid matter, it was possible to form a thincolor filter 25. As a result, it was possible to minimize the under-lensdistance and to improve the sensitivity. Further, it was possible toprevent the generation of color uneven that may be caused by theconfiguration of the edge of pattern of the color filter.

In this embodiment, although a thermosetting acrylic resin was employedas a major component of the green resist as well as the blue resist thathave been formed by means of shape transcription technique employing dryetching, it is possible to employ, other than the acrylic resin, epoxyresin, polyimide resin, phenol novolac resin, polyester resin, urethaneresin, melamine resin, urea resin, styrene resin, and a mixed resincontaining one or more kinds of these resins such as a copolymerthereof.

Further, it is possible to employ a resin of high refractive index forthe green resist, thereby making it possible to adjust the refractiveindexes of the green filter pattern, the red filter pattern and the bluefilter pattern so as to make them almost the same with each other. As aresult, it is possible to obtain a solid state image pickup device whichis low in surface reflection and excellent in sensitivity.

Further, in this embodiment, although the green filter pattern and theblue filter pattern were formed by making use of a patterning techniqueusing dry etching and the red filter pattern was formed by making use ofphotolithography, only the green filter pattern may be formed by thepatterning technique using dry etching, the blue filter pattern and thered filter pattern being formed by means of photolithography.Alternatively, the green filter pattern and the red filter pattern maybe formed by making use of a patterning technique using dry etching andonly the blue filter pattern is formed by making use ofphotolithography. What is important is that the filter pattern to beinitially formed should be formed by means of dry etching and the filterpattern to be finally formed should be formed by means ofphotolithography. However, since the green filter pattern and the bluefilter pattern that have been formed by means of photolithography aremore liable to be peeled as compared with the red filter pattern, thesegreen and blue filter patterns should preferably be formed by means ofpatterning technique using dry etching.

Further, in this embodiment, although the micro-lens were formed bymeans of thermal reflow method, it is more preferable to form themicro-lens by means of patterning technique using dry etching, whichmakes it possible to reduce the under-micro-lens thickness. Thispatterning technique using dry etching is performed as follows. Namely,a transparent resin layer to be finally formed into micro-lens is formedon the surface of color filter and then a mother die of micro-lens(lens-shaped mother die) is formed thereon by means of thermal reflowmethod. Then, by making use of this lens-shaped mother die as a mask,the configuration of this lens-shaped mother die is transcribed to thetransparent resin layer by means of dry etching. It is preferable inthis case to dig away a boundary portion between neighboring filterpatterns from the surface to a depth ranging from 0.03 μm to 0.5 μmthrough the adjustment of the height of this lens-shaped mother die tobe employed in the transcription of lens configuration or through theadjustment of the etching rate by suitably selecting the material,thereby constituting the peripheral portion of micro-lens by part of thecolor filter, thus making it possible to minimize the under-lensdistance.

Incidentally, although a thermosetting acrylic resin was employed as aresin for the green resist in this embodiment, it is also possible toemploy the same kind of radiation-curing (photo-curing) acrylic resin asthe resin employed in the red resist or the blue resist. In this case,it is preferable, for the purpose of reducing the thickness of colorfilter, to reduce the quantity of a monomer or a photo-polymerizationinitiator required to be employed. More preferably, a resin which issimilar to the thermosetting resin is employed. The resin in this caseis no longer suited for use in the exposure/development process.

EXAMPLE 2

The method of manufacturing the solid state image pickup deviceaccording to this example will be explained with reference to FIGS. 8Ato 8I.

A coating solution containing acrylic resin as a major component wasspin-coated at a rotational speed of 2000 rpm on the surface of asemiconductor substrate 60 provided with photoelectric conversionelements 61 which are two-dimensionally arranged as shown in FIG. 8A.Then, the coated layer was baked by means of a hot plate for 6 minutesat a temperature of 230° C. to form a first flattening layer 62 as shownin FIG. 8B. In this case, the thickness of the first flattening layer 62was 0.45 μm.

Then, a green resist was spin-coated at a rotational speed of 1000 rpmon the surface of the first flattening layer 62 and baked for 6 minutesat a temperature of 230° C. to form a green resist layer 83 as shown inFIG. 8C. On this occasion, a green pigment represented by a color indexof C.I.PG36 was employed at a concentration of 35 wt % and the filmthickness of the green resist layer 83 was 0.5 μm. Further, athermosetting acrylic resin of high refractive index was employed as aresin or a major component of the green resist. Therefore, therefractive index of the green resist layer 63 was 1.65.

Since a thermosetting acrylic resin of high refractive index wasemployed as described above, it was possible to dispense with theemployment of a sensitizer such as a photopolymerization initiatorthough a heat-curing agent was required to be employed. Furthermore,since photolithographic properties such as alkaline-developing propertyor photo-curing property are no longer necessitated in this case, it waspossible to increase the concentration of pigment, thus making itpossible to obtain a green filter having desirable spectral propertieseven though the thickness of the green filter was reduced.

Then, a coating solution containing an acrylic photosensitive resin as amajor component was spin-coated on the surface of the green resist layer63 at a rotational speed of 3000 rpm and then formed into a pattern bymeans of photolithography to obtain a transparent resin pattern 64 asshown in FIG. 8D. In this case, since it was possible to select, as amask, a transparent resin which does not contain any substance which mayobstruct the resolution such as pigment, it was possible to perform thepatterning with high precision.

Subsequently, by making use of this transparent resin pattern 64 as amask, the green resist layer 63 was subjected to an etching treatment bymaking use of a flon gas in a dry etching apparatus, thus forming agreen filter pattern 65 a as shown in FIG. 8E. The film thickness of thegreen filter pattern 65 a on this occasion was 0.5 μm. Further, sincethe first flattening layer 62 was also partially removed, a step portionhaving a height of 0.4 μm was caused to create between the neighboringfirst flattening layers 62.

Subsequently, by means of photolithography, a blue filter pattern 65 band a red filter pattern (not shown) were successively formed to obtaina color filter 66 as shown in FIG. 8F. On this occasion, pigmentsrepresented, respectively, by a color index of C.I.PB15:6 and a colorindex of C.I.PV23 were employed in the blue resist at a concentration of30 wt % and the film thickness of the blue resist layer was 0.9 μm andthe refractive index thereof was 1.64. Further, pigments represented,respectively, by a color index of C.I.PR117, a color index of C.I.PR117and a color index of C.I.PV139 were employed in the blue resist at aconcentration of 40 wt % and the film thickness of the blue resist layerwas 0.9 μm and the refractive index thereof was 1.69.

Further, a coating solution containing acrylic resin incorporatedtherein with a UV absorber was spin-coated at a rotational speed of 1000rpm on the surface of the color filter 66 formed as described above.Then, the coated layer was baked by means of a hot plate for 10 minutesat a temperature of 200° C. to cure the acrylic resin to form a secondflattening layer 67 as shown in FIG. 8G.

Then, as shown in FIG. 8H, a lens-shaped mother die 68 formed of acrylicresin excellent in photosensitivity and in thermal reflow property wasformed on the surface of the second flattening layer 67 by means of theknown thermal reflow method.

Finally, by making use of this lens-shaped mother die 68 as a mask, anetching treatment was performed in a dry etching apparatus using afluorocarbon gas, thereby transcribing the configuration of thislens-shaped mother die 68 to the second flattening layer 67, thusforming micro-lens 69. On this occasion, a boundary portion between theneighboring patterns of the color filter 66 was etched away from thesurface to a depth of 0.2 μm, thereby accomplishing the manufacture ofthe solid state image pickup device as shown in FIG. 8I.

It was possible, through the manufacturing method of the solid stateimage pickup device as described above wherein the green filter pattern65 a was formed by means of dry etching, to form a thin color filterhaving a fine pattern and being excellent in configuration withoutgenerating the residue thereof and the peeling of pixel. Further, sincea thermosetting resin was employed in the green filter layer, it waspossible to increase the concentration of the coloring material in thesolid matter, thereby making it possible to reduce the thickness of thecolor filter and hence to obtain a thin solid state image pickup device.

In this embodiment, although a thermosetting acrylic resin was employedas a major component of the green resist as well as the blue resist thathave been formed by means of shape transcription technique employing dryetching, it is possible to employ, other than the acrylic resin, epoxyresin, polyimide resin, phenol novolac resin, polyester resin, urethaneresin, melamine resin, urea resin, styrene resin, and a mixed resincontaining one or more kinds of these resins such as a copolymerthereof.

In particular, it is possible, for the purpose of achieving a highrefractive index, to employ phenol resin, polystyrene resin, a polymeror monomer having benzene ring or aromatic ring introduced therein andalso to employ acrylic resin having a halogen atom or sulfur atomintroduced into the skeleton thereof.

By doing so, it is possible to achieve a high refractive index even inthe green filter pattern which is inherently lowest in refractive indexand relatively large in surface reflection as compared with those of theblue filter pattern or the red filter pattern. As a result, it ispossible to obtain a solid state image pickup device exhibitingexcellent sensitivity.

In the foregoing embodiment, although only the green filter pattern wasformed by way of patterning using dry etching, not only the blue filterpattern which can be easily peeled if it is formed by means ofphotolithography but also the red filter pattern which is high inconcentration of pigment may be formed by making use of dry etching.However, since it is most important that the green filter pattern to beformed at first is excellent in adhesion and in accuracy of pattern,this green filter pattern is required to be formed by making use of theconfiguration transcription technique employing dry etching. Further,the red filter pattern may be formed, as a second color, next to theformation of the green filter pattern, it is more preferable that theblue filter pattern is formed, as a second color, next to the formationof the green filter pattern, since the red filter pattern contains apigment at a high concentration, thus enabling the residue thereof toleave behind.

In this embodiment, although a step portion having a height of 0.4 μmwas formed in the first flattening layer 62 which is formed below thecolor filter 66, this first flattening layer 62 may be etched to anextent ranging from 0.03 μm to 0.5 μm through the adjustment of thethickness of the transparent resin pattern 64 to be formed into a motherdie in the formation of green filter pattern or through the adjustmentof the etching rate by suitably selecting the material. The reason forsetting the lower limit to 0.03 μm is that this value is the minimumvalue which SEM or AFM can effectively identify the thickness thereof.On the other hand, the reason for setting the upper limit to 0.5 μm isthat if the height of the step portion is exceeded over 0.5 μm, thesurface of film would be roughened giving rise to the generation ofsurface scattering, thus deteriorating the sensitivity.

Further, the micro-lens were formed by means of dry etching in thisembodiment, the micro-lens may be formed by means of the conventionalthermal reflow method. However, if it is desired to minimize theunder-micro-lens distance, the micro-lens should preferably be formed bymaking use of the configuration transcription technique employing dryetching.

EXAMPLE 3

The method of manufacturing the solid state image pickup deviceaccording to this example will be explained with reference to FIGS. 8Ato 8D and FIGS. 9A to 9E.

A coating solution containing acrylic resin as a major component wasspin-coated at a rotational speed of 2000 rpm on the surface of asemiconductor substrate 60 provided with photoelectric conversionelements 61 which are two-dimensionally arranged as shown in FIG. 8A.Then, the coated layer was baked by means of a hot plate for 6 minutesat a temperature of 230° C. to form a first flattening layer 62 as shownin FIG. 8B. In this case, the thickness of the first flattening layer 62was 0.4 μm.

Then, a green resist was spin-coated at a rotational speed of 1000 rpmon the surface of the first flattening layer 62 and baked for 6 minutesat a temperature of 230° C. to form a green resist layer 83 as shown inFIG. 8C. On this occasion, a green pigment represented by a color indexof C.I.PG76 was employed at a concentration of 40 wt % and the filmthickness of the green resist layer 83 was 0.5 μm. Further, athermosetting acrylic resin of high refractive index was employed as aresin or a major component of the green resist. Therefore, therefractive index of the green resist layer 63 was 1.65.

Since a thermosetting acrylic resin of high refractive index wasemployed as described above, it was possible to dispense with theemployment of a sensitizer such as a photopolymerization initiatorthough a heat-curing agent was required to be employed. Furthermore,since photolithographic properties such as alkaline-developing propertyor photo-curing property are no longer necessitated in this case, it waspossible to increase the concentration of pigment, thus making itpossible to obtain a green filter having a reduced thickness.

Then, a coating solution containing an acrylic photosensitive resin as amajor component was spin-coated on the surface of the green resist layer63 at a rotational speed of 3000 rpm and then formed into a pattern bymeans of photolithography to obtain a transparent resin pattern 64 asshown in FIG. 8D. In this case, since it was possible to select, as amask, a transparent resin which does not contain any substance which mayobstruct the resolution such as pigment, it was possible to perform thepatterning with high precision.

Subsequently, by making use of this transparent resin pattern 64 as amask, the green resist layer 63 was subjected to an etching treatment bymaking use of a flon gas in a dry etching apparatus, thus forming agreen filter pattern 65 a as shown in FIG. 9A. The film thickness of thegreen filter pattern 65 a on this occasion was 0.5 μm. Further, aportion of the first flattening layer 62 which was not covered by thegreen filter pattern 65 a was completely removed.

Subsequently, by means of photolithography, a blue filter pattern 65 band a red filter pattern (not shown) were successively formed to obtaina color filter 66 as shown in FIG. 9B. On this occasion, pigmentsrepresented, respectively, by a color index of C.I.PB15:6 and a colorindex of C.I.PV63 were employed in the blue resist at a concentration of30 wt % and the film thickness of the blue resist layer was 0.9 μm andthe refractive index thereof was 1.64. Further, pigments represented,respectively, by a color index of C.I.PR117, a color index of C.I.PR117and a color index of C.I.PV139 were employed in the blue resist at aconcentration of 40 wt % and the film thickness of the blue resist layerwas 0.9 μm and the refractive index thereof was 1.69.

Further, a coating solution containing acrylic resin incorporatedtherein with a UV absorber was spin-coated at a rotational speed of 1000rpm on the surface of the color filter 66 formed as described above.Then, the coated layer was baked by means of a hot plate for 10 minutesat a temperature of 200° C. to cure the acrylic resin to form a secondflattening layer 67 as shown in FIG. 9C.

Then, as shown in FIG. 9D, a lens-shaped mother die 68 formed of acrylicresin excellent in photosensitivity and in thermal reflow property wasformed on the surface of the second flattening layer 67 by means of theknown thermal reflow method.

Finally, by making use of this lens-shaped mother die 68 as a mask, anetching treatment was performed in a dry etching apparatus using afluorocarbon gas, thereby transcribing the configuration of thislens-shaped mother die 68 to the second flattening layer 67, thusforming micro-lens 69. On this occasion, a boundary portion between theneighboring patterns of the color filter 66 was etched away from thesurface to a depth of 0.1 μm, thereby accomplishing the manufacture ofthe solid state image pickup device where an upper portion of the colorfilter was employed to constitute part of the micro-lens as shown inFIG. 9E.

It was possible, through the manufacturing method of the solid stateimage pickup device as described above wherein the green filter pattern65 a was formed by means of dry etching, to form a thin color filterhaving a fine pattern and being excellent in configuration withoutgenerating the residue thereof and the peeling of pixel. Further, sincea thermosetting resin was employed in the green filter layer, it waspossible to increase the concentration of the coloring material in thesolid matter, thereby making it possible to reduce the thickness of thecolor filter and hence to obtain a thin solid state image pickup device.

In this embodiment, although the first flattening layer 62 disposedbelow the filter pattern that will be formed by way of patterning usingphotolithography was completely removed, the first flattening layer 62may be partially left remain through the adjustment of the thickness ofthe transparent resin pattern 64 to be formed into a mother die in theformation of green filter pattern or through the adjustment of theetching rate by suitably selecting the material. However, if it isdesired to prevent the existence of residue of the color filter layer ofthe second color or the third color, the first flattening layer 62should preferably be completely removed.

In this embodiment, although the micro-lens was formed by means of dryetching, the micro-lens may be formed according to the conventionalthermal reflow method. However, if it is desired to minimize theunder-micro-lens distance, the micro-lens should preferably be formed bymaking use of the configuration transcription technique employing dryetching.

In this embodiment, although the boundary portion between theneighboring color filters was etched to a depth of 0.1 μm from thesurface and the peripheral portion of the micro-lens was constituted bypart of the color filter, this boundary portion may be etched to a depthranging from 0.03 μm to 0.5 μm depending on the height and materialselected of lens-shaped mother die or depending on the material selectedbased on the construction, thickness and etching rate of the layer towhich the lens configuration is transcribed. The reason for setting thelower limit to 0.03 μm is that this value is the minimum value which SEMor AFM can effectively identify the thickness thereof. On the otherhand, the reason for setting the upper limit to 0.5 μm is that if theheight of the step portion is exceeded over 0.5 μm, the surface of microlens would be roughened giving rise to the generation of surfacescattering, thus deteriorating the sensitivity.

1. A method of manufacturing a solid state image pickup device comprising photoelectric conversion elements which are two-dimensionally arranged in a semiconductor substrate, and a Bayer arrangement color filter comprising a plurality of color filter patterns differing in color from each other and disposed on a surface of the semiconductor substrate in a position corresponding to the photoelectric conversion elements, wherein said plurality of color filter patterns are formed by successively patterning a plurality of filter layers differing in color from each other, the method comprising: dry etching a first color filter layer that contains a thermosetting resin through an etching mask to form a first color filter pattern of the plurality; and then successively forming the rest of the color filter patterns of the plurality, the formation of each of the rest of the color filter patterns comprising: forming a color resist layer containing a photosensitive resin on the semiconductor substrate; subjecting the color resist layer to a patterning exposure to selectively photo-cure the color resist layer; and subjecting the color resist layer to a development using a developing solution to remove an uncured portion of the color resist layer and form the filter pattern.
 2. The method according to claim 1, wherein forming the first color filter pattern further comprises: forming a photosensitive resin layer on the first color filter layer; patterning the photosensitive resin layer to form a resin pattern; performing the dry etching by using the resin pattern as the etching mask to transcribe a configuration of the resin pattern to the first color filter layer, and wherein the first color filter pattern is the largest in area among the plurality of color filter patterns. 